Radio-frequency joint



Oct. 19, 1948.v w. w. sALlsBuRY mmm-FREQUENCY JOINT- Fled June 5, 1943 5 Sheets-Sheet 1 l/Il 8 FIG. 4

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mvENTOR BY W7; a//s 15u/'- Oct. 19, 1948. w, w, sALlsBURY 2,451,876

RADIO-FREQUENCY JOINT Filed June 5, 1943 5 sheets-snee; 2

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lNvr-:NTOR BY w. maf/mbar] Oct. 19, 1948. .w. w. sALlsBURY 2,451,876

RADIO-FREQUENCY JOINT Filed June `5, 1945 5 Sheets-Sheet 4 iNvENTOR BY W. W //SU/ 7 '4'6" 'l Oct. 19, 1948.

Filed June 5, 1943 5 Sheets-Sheet 5 FIG 2O T 7c V/ l :ll/l// 5 IIIIIIIIIII//IIlIIIIIlIIIIlIII/l I lll/11111111 l. ly /Y \NVENTOR B-Yw. /f b ,j

'cal contact. additional diillculties Patented oec-19, 194s 'UNITED vSTATES PATENT oFFicE "1 aspro-Fritor Jonvr I I winnend w. seinem-y. Arlington, by mesne assignments, to the America as represented by the Navy Mass., assigner, United States of Secretary of the Application June 5, 1943, Serial No. 489,844l

(ci. 11s-w 25 claim.

This invention relates to systems for the transmission and .reception of high-frequency radio waves. It is especially concerned with the miniform Aof rotating joint in accordance' with the mizing of the discontinuities caused by joints in y tions occurring even when the conducting members in question are held in relatively good physiarise because of the variability of the effectiveness of the contact when subjected to vibrations, atmospheric action, sliding movements or adjustments,and so on.

It is an object oi' this invention to provide a structure which is' adapted to avoid contact losses and to establish a high quality radio frequency conducting relationship between twol physically distinct conducting elements which are intended to carry current or guide waves to and/or from each other. It is a further object of this invention to provide means forreducing the losses in the transmission of high frequency electromagnetic present invention:

Fig. is a longitudinal cross-section of one form of an adjustable terminating closure for coaxial conductor transmission lines;

Fig. 1l is a longitudinal cross-section of another form of adjustable terminating closure for coaxial conductor transmission lines;

Fig. 12 is a longitudinalcross-section of an articulated joint embodying the present inven-v tion; a

Fig. 13 is a cross-section oi' a high-frequency i heterodyne mixer apparatus .in which is embodied means in accordance with the' present invention for establishing an apparent radio frequency conducting relationship-between two elements thereof without actual electrical contact:

Fig. l4 is a longitudinal cross-section of a joint" according to the present invention between two sections of wave guide pipe;

Fig. 15 is a longitudinal cross-section of a rotating joint for wave guide pipe in accordance with the present invention;

Fig. 16 is a longitudinal cross-section of an adjustable closure for a wave guide pipe constructed according to this invention:

Fig. 16A is a transverse sectional view along the line I-I of Fig. 16;

Fig. 17 is across-section of a structure for providing an adjustable loading capacitance in a wave guide-pipe; Y

energy between components of high-frequency radio systems. Still a further object of this inlosses in adjustable or movable parts of highfrequency radio systems by avoiding contact losses and thereby to make possible greater use of such components. The manner in which the invention is carried out is best explained with reference to the drawings, in which:

Figs. 1, 2, 3 and 4 are diagrams illustrating the principles o the invention;

Fig. 5 is a longitudinal cross-section of a rotating joint embodying the present invention;

Fig. 6 is a longitudinal cross-section of another fom of rotating joint embodying the present invention;

Fig. 7 is a longitudinal cross-section of a modlcation of the apparatus shown in Fig. 5;

Fig. 8 is a` longitudinal cross-section of a form of joint in accordance with the present invention;

Fig. 9 is a longitudinal cross-section of another Fig. 18 is a' cross-section of a variant form of the type of apparatus shown in Fig. 17;

Fig. 19 is a cross-section of a structure for mounting a crystal detector across a wave guide pipe. and

Fig. 20 is a diagram illustratingthe principles of a modified form of structure according to the present invention. 4

Figs. l, 2, 3 and 4 show, forl purposes of illustration of the principles of this invention, pairs' of metallic structures between the lower surfaces of which it is desired to establish an electrically.

conducting relationship for high-frequency electromagnetic oscillations, which is to say that it is desired to establish conditions ior energy transfer between the members of each pair at high i.'re` quencies with as low losses as possible. The lower surfaces of the metallic structures shown in these nngures may be considered as current-carrying surfaces or they may be regarded as wave guiding surfaces which guide electromagnetic waves in their immediateneighborhood. 0n Fig. 1,1 the current-carrying and wave guiding surfaces are shown at 2 and 3, being located respectively on the l bent over as shown in Fig. 1. 'in Fig. 4, the gap 6 may form structures are not preferred because of their larger physical dimensions and because of the greater amount of frequency sensitivity which they exhibit. y

The particular geometrical configuration of the gap B. the branch channel 1 and the surfaces 2 and 3 are by no means limited to the arrangement shown for purposes o'f illustration in Fig. 1. The gap 6 itself may be bent and the branch channel 'I may form with part of the gap 6 a straight channel. as shown inFig.- 2, for instance. Or again, as shown in Fig. 3, the branch channel Il may extend away from the gap 6 without being a channel which is bent on itself between A tion with the branch channel 1, which inV Fig. 4 as in Fig. 2 forms a; continuation oi' the gap In Figs. 2 and 4 the gap 6 leads to the outside through the opening' 8a whichcorresponds to the opening 8b on Figs. 1 and 3. The size of lthis opening is 'not important and'I it may, if desired, be sealed by material of any conductivity.

Arrangements such as those shown diagrammatlcally in the above-described gures are par- Again, as shown' its mouth and its June-- 6 by relative rotation of the transmission line about their common axis.

The 'eifectiveness of the radio frequency connection just constituted between the conductors J I2 'and Il is at a maximum at the frequency for which the electrical quarter-wave length dimension above mentioned exactly obtains. It is possible to establish a reasonably good radio frequency connection between the conductors for a range for frequencies in the neighborhood of the l said frequency by properly dimensioning the transverse width of the resonating channels. Thus in the apparatus of Fig. 5 the annular channel 2| is narrow whereas the annular cavity enclosed by the cup member is relatively large,

DThus the coaxial conductor transmission line at Ill with an inner conductor II and an outer conductor I2. The other of these "transmission lines appears at I3, having an inner conductor It and an outer conductor I5. Insulating beads I5 serve tosupport the inner conductorsofthe respective transmission lines from the corresponding outer conductors in suitable electrical isolation.

quarter of the open air wave length for the fre-4 quency in question.

'I'he inside of the cup'- shaped member 20, since the member .20 is in acteristic impedance.

' is somewhat different from constituted by the outer part of the sleeve' 20 and the conductor I8 will have a low characteristic impedance, whereas the coaxial conductor transmission line formed by the inner surfaces of cup member 20 will have a substantially higher characteristic impedance. It is well known that the input impedance of a transmission line which is terminated by an impedance other than its charwhen losses are neglected, will be proportional to the characteristic impedance of the 'transmission line as well as to a trigonometric tangent function determined by the frequency. Thus. because of its relatively high] characteristic impedance, the short-circuited transmission line constituted by the inner surfaces of the cup member 20 will havev a relatively high impedance even when the frequency is such that the length of this vtransmission line an electrical quarter-wave length. In order to cause the transmission line constituted by the outer surface of the cup member 20 and the inner surface oi' the conductor I8 to appear to be substantiallyl open circuited, the impedance at the rear edge of the cup member 20'need only be large relative to the characteristic impedance of the latter transmission line, which', as before pointed out, is relatively low. Se long as this is the case. an impedance will be presented at the mouth 22 of the annular space 2I which is small even relative to the. already small characteristic impedance of the transmission line constituted by the outer surface of the sleeve 20 and the inner surface of theconductor I8. In the device shown in Fig. 5. cbnsequently. good energy transferring relationship 'is established between the conductors I2 and AI5 for a substantial range of frequencies in the neighborhood of the desired midrange frequency.

- Referring 'tovFigsL 1. 2,;3, and 4, the foregoing explanation-of the operation of the apparatus annular shape, thus defines a resonant chamber corresponding to the branch channel 1 of Figs. 1, 2, 3 and 4. The inside of thecup member 2l communicates around the backv of the said member with an annular gap 2| between the outside of the cup member 20 and the tubular conductor I8. v The annular gap -2I thus corresponds to thegap 8 of Figs. 1, 2, 3 and 4. By virtue of the above-defined axial length of the cup member 20, the cup member 20 and the conductor II are caused to act at the frequency in question asif a high quality electrical contact existed between them across the annular mouth 22 of the gap 2|. 'I'he conductors I2 and I5 are thus eectively brought into energy-transferring relav tion for the high frequency in question 4and it shown in Fi'g.15` shows that for operation of ap- 60 .paratus in 'accordance that thegap .B ,should have-a relatively low charwith the present invention over a range of frequencies it is desirable acteristic impedance with regard to the propagation of electromagnetic waves towards the branch channel 'I'and that the branch channel 'I should have a relatively high characteristic impedance with regard to the propagation of electromagnetic waves between its Junction wit the gap 6 and the terminating closure 8. In the apparatus of Fig. 5. in order to maintain the alignment of the axes -of the transmission lines Ill and I 3 in-the immediate neighborhood of the rotating joint, bearings in the form, of annular porous oil-bearing masses 2l and 24 are provided between the` outer surface of the conductor i6 and the inner surface of an extension 25 of the conductor I8. I! desired, pressure-sealing means may be provided in the space 28 between the bearings 28 and 24, an arrangemew which is desirable when the coaxial conductor transmission lines are filled with compressed air to increase the breakdown voltage. An annular metallic block mounted on the outside of the conducto: l at a short distance in bach of the cup-shaped member 2t is shown at t. The use of this type of block is preferred as it is believed that it aids the eiectivencss of the cup-shaped member 2t and reduces corrie-a what the energy loss at the joint. The block @d is not. however, necessary for the operation of the device and results satisfactory for marry purposes may be obtained without the use of such a structure ii for some reason that structure should be inconvenient. The amount of improvement to be obtained by the use of a structure such as the block 2@ depends to some extent upon the nature ci the structure in baci: ci the cupshaped member 2t or its equivalent.

The inner conductors li and it are brought into eiective energy transferring relationship by a structure operating on a principle diiierent from that described above. The conductor ii is broadened out by means of a conical section 3b andextended in the form of a tube 53E. The conductor it projects within the tube @i as shown at tit. The length of the conductor ifi which projects as at 322 into the tubular conductor til is substantially a quarter-wave length. Since a quarter-wave iength transmission line is thus formed with the farther and open-cir suited, the nearerend, at the mouth of the ennuiar space between the conductor it and the tube 3l, oiiers a very low impedance. The series reactance interposed between the conductors li and it by the structure ti, t2 not only passes through zero at the frequency for which the quarternvave dimension holds, but it also changes relatively slowly with frequency (or, conversely, with slight changes in length of the overlap between the conductors lll and 3l) under these conditions.

The flare of the conical structures il@ and it and the relative radii of the tubular structures ti and it are so constructed as to create a minimum of discontinuity with respect to the trans mission line it. in other words, the conlgura tion of the structure is designed to maintain a characteristic impedance equal to the characteristic impedance of the transmission line it in accordance with the well-known dependence of the characteristic impedance of a coaxial conductor transmission line upon the ratio of the inner diameter of the outer conductor to the outer diameter of the inner conductor.

A flange 3b is provided suitably fastened to the structure I8, i9 and to the conductor l2 for the purpose of mounting the apparatus upon a suitable support. Bolt holes for such mounting are shown at 3%.

Fig. 6 shows an improved form of rotating joint operating essentially in the manner oi the apparatus shown in Fig. 5 but better adapted for compact construction. The two transmission lines which it is desiredv to connect by a joint permitting relative rotation are shown at l0 and M, the transmission line 40 having an inner conductor 42 and an outer conductor 43 and the transmission line Iil having an inner conductor M and an outer conductor 5. The transmission ,lines 40 and 4i are shown provided with couplings 0B adapted for coupling? or said transmis sion lines to further sections of transmission line or to other radio apparatus. The cup-shaped member 48 mounted upon the outside of the conductor Ib corresponds to the cup-shaped member l2@ shown in Fig. 5. The annular interior of the member dit, is, however. filled with a solid dielectric. preferably polystyrene as shown at Mia. The presence of the said dielectric acts to shorten the physical length oi an electricalguarter-wave length in a similar structure having air dielectric'. Thus it is possible t0 construct a structure oi the coniluration oil Fig. o in which the inside of the cup member t@ will define an electrical quarterwave length and the channel il@ around the outside oi the cup member itl will also define an electrical quarter-wave length between the bach oi. the cup member it and the nearest approach of the-conductors lil and tb. The length of the latter path is longer than the axial dimension of the cup member but since the dielectric is air, the above-described relation may be established. The radial dimension of the cup member t@ may be designed to provide the above-men tionecl relation between the electrical wave length in the dielectric-filled interior of the cup member and inthe air-filled channel around the outside of the cup member dfi. As shown on Fig. d the housing structure d@ .which is securely fastened upon the conductor i9 cooperates with the cup member lil to define an annular gap dit.

Behind the cup member @il ball bearings lli are mounted between the conductor dit and the housing t@ to facilitate relative rotation oi the members ci' the joint. A resilient gasket b2 is preferably provided between the ball bearings and their associated races and the housing tt. Each oiJ the ball bearings is provided a pressure seal for maintaining the pressure within the coaxial conductor line system irrespective ofthe atmospheric pressure. The pressure seal mechanism includes the threaded rings 53 and t, the sleeve @52, thegasket tit and the bevel ring ill. The gasket ii@ is preferably made ci a compressible or resilient material such as chloroprene or a similar material, such as butadiene derivatives and materials known to the trade as neoprene" and Duprene The inner conductors i2 and fifi, which are supported relative to the corresponding outer conductors by means ci' the insulators Gil, are brought into effective energy-transferring relationship in a manner similar to that shown in Fig. 5 in connection with the conductors il and it. Because of the greater thickness of the inner conductor in the transmission line shown in Fig. 6, it is unnecessary to spread either oi the inner conductors in the apparatus of Fig. 6, the conductor dll being simply axially bored at its end to define a cavity 82 into which an extension @il of the conductor l2 projects without establlslxu ing contact therewith. The length of the extension 83 within quarter-wave length so that energy-transfez'rins,r relationship between the conductors d2 and it is established as described in connection with Fig. 5. More accurately speaking, the length ot the channel between the conductor 42 and its extension '63 on one hand and on the other hand the conductor dt is an electrical quarter-wave length. The said channel includes not only a portion extending in a generally axial direction but also a small radial portion between the extremity of the conductor d4 and the conductor 42, which radial portion should be taken into account. It

the cavity 62 is an electrical Axial length of polystyrene block 48a..

there has been found that the desired electrical been fo'und suitable in practice. The dimensionsv given are generally applicable to wave lengths in the microwave range, at least.l but it is to be understood that they may beinterdependent. so that if the diameter of the conductors 42. 4I, 44 and 40 are varied in terms of wave length, corresponding changes in the Joint structure should preferably be made for best results, although the frequency sensitivity of the Iioint is low enough so that the dimensions in question are not extremely critical.

Table I Description of dimension l) Outer diameter of conductors 42 and 44 Inner diameter oi conductors 43 and 40 Gap between conductors 43 and 46 Dimension a (see Fig. 6) Outer dla l' 03..' Diameter oi recess 62 The following table gives illustrative dimensions for the arrangement shown in Fig.

f Table 11 inside-- Axial length of cup member 20 outsldeu Outer diameter of conductors 11 and 14--- 0.032 Inner diameter of conductors 12 and 15--- 0.144 Inner diameter of tube 18 0.416 Outer diameter of 31 0.112

Inner diameter of 3l 0.096

Overlap between 14 and 31 0.18

Fig. l shows a form of rotating Joint for coaxial conductor transmission lines essentially similar to that shown in Fig. 5 except that the cup member 20 is replaced by a double cup member comprising a sleeve bearing two cup-like flanges 1l and 12. The sleeve 10, like the inner sleeve of the cup member and 48 in Figs. 5 and 6 respectively, is provided for ease of assembly and could ofcourse be dispensed with. in which case the cup-like flanges would be fastened, preferably soldered. directly to the outer conductor Il. Although in most cases a second cup section such as is provided by the member) 12 is unnecessary it may be of advantage to employ such a member where a very great reduction of the energy loss to the system at the rotating Joint is desired. Multiple resonant choke sections arrangement `such as in Fig. 'l may also have advantages for operation over a range of frequencies if the two resonator sections are tuned to neighboring but slightly diil'erent frequencies. v

Theoretically. in order that both cup members 1i and 12 may respectively act to produce an apparent short circuit for radio frequencies at the mouth 22 of the channel system 1I, 14, the front of the member 12 should be spaced from the quarter-wave length relationship is obtained in l0 back of the member 1i by a quarter-wave length. Rotating joints with such spacing between the members 1I and 12 have been found to operate satisfactorily but experimental results have shown that closer spacing between the two cuplike elements will give equally good results and in some cases slightly better results and are moreover more convenient in many cases because of their greater compactness. In the type of construction shown in Fig. 7, where the spacing between the cup elements 1| and 12 is less than a l quarter-wave length the cup member 12 may be lli regarded as producing an apparent radio frequency short circuit at the mouth 10 of the channel 14, thus tending to eliminate any residual radio frequency voltage that may appear across the annular gap 10 in spite of the action of the cup member 1I. Thus, in the arrangement of Fig. 7, the element 12 apparently does not itself contribute appreciably to creating an apparent short circuit at the mouth 22 of the channel 13 but does assist to reduce the amount of energy which is able to "leak out of the system at the rotating joint. For most purposes the effective ness of a single cup member is so high that a single section arrangement such as that shown in Fig. 6 is preferable.

Fig. 8 shows a form of ioint for coaxial conductor transmission lines which is particularly compact and is adapted for both fixed and rotating Joints. 'Ihe inner conductor ioint is similar in physical configuration to that shown in Fig. 6 between the conductors 42 and- 4.4. 'I'he outer conductor joint is effected by means of two forwardly projecting sleeves 200 and 20|V mounted upon oneof the outer conductors which is shown at 202. The sleeve 200 is adapted to project over the other outer conductor 203 in such a manner as to leave a small clearance 204 communicating with the gap 205 between the extremities of the conductors 202and 202. The outer sleeve 20| is so shapedy as to provide an annular space 200 between it and the sleeve 200 having an axial depth of-an electrical quarter-wave length and a transverse width or clearance preferably several times as great as the clearance between the sleeve 200 and the conductor 203. Any impedance which may appear at the extremity of the sleeve 20| and the conductor 208 will appear across the clearance 204 only in series with the high impedance at the mouth of the annular space 200 at frequencies in the range o1 desired operation, so that a -low impedance will be presented across the gap 205 and energy transferring relationship will thus be established between the conductors 202 and 203. Means for supporting the various conducting structures with respect to each other have been omitted in Fig. 8, as in Fig. 1, to promote simplicity of illustration. It is to be understood that various well-known types of l mechanical joint may be provided to maintain the desired physical relationship between the conductors 202 and 203. Since the type of ansmission 'line joint shown in Fig. 8 does not rccfuire any actual physical contact between the corresponding conductors of the two coaxial conductor transmission lines being joined, and since a vshock-absorbing or elastic physical mounting maybe employed yto keep the two coaxial conductor llne's in general alignment and proximity, this type of joint is useful for isolating part of' the electrical system from mechanical shock which would otherwise be transmitted from other parts oi the system. The one oi the coaxial conductor transmission lines shown in Fig. 8 might be rigidly connected to a dellcatevapparatus. such as a transmitting tube. andthe joint may then be used to transfer electric energy to or from such apparatus while isolating the apparatus in question Afrom mechanical shock. The said delicate apparatus together with the portion of transmission line connecting it to the iointcould be sheltered in a shock-absorbing mounting. Small relative motion between the members of the joint shown in Fig. 8 may be permitted without serious interference to the electrical properties of the joint. A

Fig. 9 shows a Joint similar to the joint ot Fig. 8 provided with ball bearings for service as a rotating joint and incorporating an inner conductor joint constructed in accordance with th'e present invention instead of the type of inner conductor joint above described (which I have claimed in a copending application). The apparatus shown in Fig. 9 is provided with a pressure sealing arrangement 2li of the type known to the trade as "Garlock number 95." Seal 2l I is an annular washer made of a iibrous, leather-like material tightly pressed into the annular opening defined by the outer conductor of the coaxial line and the inner surface of the bearing housing. and held in place by an annular retaining washer as shown. The provision of the said pressure sealing means permits the maintenance of an air pressure inside the coaxial conductor transmission line system which is higherthan that on the outside of said transmission line which serves the purpose of inhibiting the occurrence of corona discharges and at the same time tends to prevent penetration of water or dust from the outside into the system.

In the apparatus shown in Fig. 9 the inner conductors of the coaxial conductor line which are joined by the rotating joints are supported by stub-line supports 2i2. These stub-line supports are essentially branch transmission lines of a length ofapproximately a quarter-wave length terminated at their extremities by a 4short-circuiting plug 2i3. The stub-supports in this case are of a demountable type. The inner conductors of the stubs each comprise a sleeve 2H and a machine screw 2i5. The sleeve 2M is preferably soldered to the plug 2I3, since good electrical connection is desired at the short-circuited end of the stub line, where currents may be relatively heavy. The machine screw 2i5 ts inside .the sleeve 2i@ and is threated into one of the transmission line inner conductors 2I6 and 2li. Tightening the machine screw 2lb brings the inner conductor in question into good mechanical and electrical contact with the sleeve 2id. A soldered joint is not necessary at this point since little current lows in and out of -the stub because of its quarter-wave length dimension.

The inner conductor joint in the apparatus of Fig. 9, connecting the conductors 2i-6 and Ril is constituted in a different manner from that of the inner conductor joint previously shown for coaxial conductor lines. Instead of employing a simple open-ended quarter-wave line connection, a system of annular cavities designed in accordance with the present invention is provided. The conductor 2 I 'i projects for an electrical quarterwave length into a tubular extension 250 of 'the conductor 2i5, with a relatively narrow clearance, thus constituting a coaxial conductor transmission line of a length of an electrical quarterwave length. The narrow clearance between the conductor 2I1 and the extension 250 of the conductor 2IB is continued into 8. wider diameter within the end o! the conductor annular cavity 25| between the extension 250 and an inner central projection 252 of the conductor 2i6. The cavity 2M has an axial length of an electrical quarter-wave length, so that it cooperates with the previously mentioned narrow annular clearance to establish a low radio frequency impedance between the conductor 2 I 1 and the extremity of the tubular extension 250 across the gap 253, and this for a range of frequency in accordance with the principles above described.v In order that the narrow annular clearance between the tubular'member 250 and the conductor 2i1 may be maintained, the central projection 252 is adapted to grip a projecting pivot pin 2M preferably made of hardened and ground steel, which projects into a recess 255 of relatively lazrlg'e In this recess is provided a suitable bearing 25B in which the pin 254 is adapted to turn and which centersthe pin with respect to the conductor 2li. I prefer to make the bearing 26B of a graphitebearing cadmium alloy. In accordance with the principles oi' the present invention, the electrical properties oi the bearing material are unimportant because such material appears across the narrow clearance only in series with the open end of a quarter-wave resonator.

Figs. 10 and 11 illustrate the application of the present invention to the construction of movable terminating closures or plungers" for coaxial' conductor transmission lines. Such structures have great utility for tuning coaxial conductor line systems, especially in such devices as double stub tuners and wave meters. Adjustable closures of thesimple electrical contact type introduce excessive losses while those of the quarter-wave cup type may introduce reilections at points other than the desired termination, because of their configuration. Adjustable closures constructed in accordance with the present invention provide the effect o f a straight ter-l minating wall across the coaxial conductor line in question, without the introduction of contact losses.

Referring to Fig. 10, 220 is the inner conductor .and 22| is the outer conductor oi a coaxial conductor line which itis desired to tune or terminate by an adjustable short-circuiting closure. For this purpose a slider 222 is mounted upon the conductor 220 in a manner adapted to permit axial displacement along 'the conductor 220. The

slider is adapted to be actuated by means of al rack 223, which, may be driven by a suitable adjusting mechanism. The slider 222 carries a forwardly projecting conducting sleeve 224 which is locatedapproximately midway between the conductors 229 and 22i. The sleeve 224 carries at its forward extremities an annular conducting structure 225 upon which are mounted two con-4 ducting sleeves 228 and 227, the former being positioned close to, but spaced from, the conductor 220 and the latter being positioned close to, but spaced from, the conductor 22i. The, sleeves 228 and 221 are each of a length of substantially a quarter-wave length preferably of a frequency in the middle of the range of frequencies at which operation of the Adevice is intended. The axial dimension of the annular structure 225 is so determined that the path around the rear ends of the sleeves 226 and 221 and down between the said sleeve and the supporting sleeve 226 to the rear face of the annularl structure 225 will likewise be an electrical quarterwave length long. The spaces between the sleeves 228 and 224 and between the sleeves 221 p 13 and 224 are relatively wider than the spaces between tlie sleeve 223 and the conductor 22| and between the sleeve 221 and the conductor 22|, in order that the device will provide the desired short-circuiting clsure eii'ect at a range of frequencies, instead of substantially a't one frequency only.

In accordancewith the principles of the present invention an apparent radio frequency short circuit will be established between the conductor 228 and the lower or forward end of the sleeve 223, and likewise between the conductor 22| and the lower or forward end of the sleeve 221, with respect to energy fed to the line 228, 22| from below. Thus a radio frequency short circuit will be established between the conductors 220 and 22| in the plane of the front face of the annular structure 228. The location of this short circuit may be varied by moving* the entire terminating closure structure by actuating the rack 223 and displacing the slider 222. The small clearances between the .quarter-wave sleeves and the conductors of the transmission line do not in practice give rise to undesired sparking or corona, even at their rear extremities. Structures ofthis type may thus advantageously be employed even in systems operating at high power. Joints and closures of the types herein described are opera- Ytive at relatively high power partlyv because of the fact that the voltage across the narrow clearances is not as high as that across the transmission line with which the apparatus is associated. on account of the dependence of the voltage amplitude in a resonant transmission line `upon the characteristic impedance of the line.l Since the characteristic impedanceof the lines having narrow annular clearance is low and these lines current fed," the voltage developed in them will be relatively low even for such currents as the main transmission line may carry when operating at full power rating.

In order to facilitate the construction of the terminating closure for coaxial conductor transmission line in the form shown in Fig. 10, it is convenient first to solder the sleeves 228. 224, and 221, preferably by hard soldering and in the order given, to ythe annular structure 228 and then to hold the sleeve 221 in a chuck for boring the inner hole of the sleeve 228 to the desired diameter and for reaming the central hole of the slider 222 to its proper dimension, these holes being kept in line. In this manner concentricity of the outer surface of the sleeve 221, the inner surface of the sleeve 228 and the inner surface of the slider 222 may be practically assured.

Fig. 11 illustrates another type of terminating closure in accordance Withthe present invention. This type of closure employs insulation across the coaxial conductor transmission line and is, therefore, not preferred for high power operation. Because of its compact and simple structure, however, it is particularly suitable for use in a wave meter. The annular structure 238 corresponds to the annular structure 228 of Fig. 10. The sleeves 23| and 232 correspond respectively to the sleeves 228 and 221. Instead of a central supporting sleeve, mechanical support for the strucof the insulation 234. 233 between the sleeves 23| and 232. an electrical quarter-wave length in the space between the said sleeves will be physically shorter than if the said space were nlled only with air and in consequence the actual dimension of the annual lstructure 233 is somewhat greater than that of the annular structure 22| for a given frequency of operation. The sliding closure is mechanically actuated by means of rods 240 and 24| threaded into the insulating structure 234 and fastened at their other end in a crosshead 242. The crosshead 242 is adapted to be advanced or retracted in response to turning of a shaft 243 mounted in ball bearings 244 in the crosshead 242 and threaded at its extremity into the end of the inner conductor 233 of the transmission line to be terminated. A knob 248 mounted on the shaft 243 may be provided for facilitating manipulation of the shaft and for furnishing a micrometer reading. Additional indication of the position of the terminating closure may be furnished by 'a sleeve 243 mounted on the crosshead 242 and slipping over I the outer conductor 238. The indication may be furnishedby a scale marked on that part of the outer conductor 289 which is covered and uncovered by the movement of the crosshead 242.

In the apparatus of Fig. 11, the branch channels (i. e. corresponding to the channel 1 of Fig. 1) of the two annular resonating structures designed to achieve the establishment of radiofrequency short circuit are combined into a single quarter-wave resonator which communicates bothv with the annular space between the sleeve 23| and the conductor 238 and with the annular space between .the sleeve 232 and the conductor 238. in each case so communicating at a point approximately an electrical quarter-wave length from the desired electrical closure. This illustrates another of the many variations in physical structure which may be made in the design of apparatus for operation in accordance with the principles of the present invention.

Fig. 12 shows an articulated joint for coaxial conductor lines in which advantage is taken of the present invention. This joint is designed to provide freedom for wobbling movements which may include small amounts of relative angular movements of the axes of the coaxial conductor lines as well as small amounts of relative translatory movements back and forth.

In the apparatus of Fig. 12 it is desired to effect .a joint between the transmission line 11 which comprises the inner conductor 18 and the outer conductor 18, and the transmission line 88 which comprises the inner conductor 8| and the outer conductor 82. In this case the inner conductors as well as the outer conductors of the transmission line 11 and 80 are provided in hollow form. the purpose being to provide lightness of construction. The transmission line 11 is expanded into the transmission lines 11a and 11b in two steps. In the first of these steps the conductor 18 connects through the ring 85 with the tubular conductor 86 which together with the inner conductor 18 form the transmission line 11a. In the second step the conductor 86 connects through the annular structure 81 to the conductor 88 and the inner conductor 18 connects through the annularstructure 88 with the tubular conductor 80, the conductors 80 and 88 forming the transmission line 11b. The lengths of the transmission lines 11a and 11b and the radii of their respective conductors are so provided as to reduce the total resultant reflection effect -of the various changes in transmission line dimensions between the end of the transmission line 11 and the articulated joint at the opposite end of the transmission line 11b in accordance with well-known principles. The transmission line 11a accordingly has a length of approximately a quarter-wave length and the transmission line 11b has aY length of approximately a half-wave length.

The transmission line 80 is built out into the transmission lines 80a and 80h inlsuccession by connecting the conductor 82 to the tubular conductor 82, of larger diameter, and in turn connecting the conductor 82 to the tubular conductor 88 which has a still larger diameter. The

. aforesaid connections are made by means of the annular conducting and supporting structures 84 and- 88 respectively. As in the case of the transmission lines 11a and 11b. the transmission line 80d is so dimensioned as to reduce the total resultant reflection occurring between the transmission llne 80h and the transmission line 80 in accordance with well-known principles. Thus the transmission line 80a is a quarter-wave length long.

An annular boss 81 is provided on the outside of the conductor 88 for engagement with the conductor 88 in order to maintain the desired physical relationship of kthese conductor-s. The boss 81 may conveniently be made of brass and soldered to the conductor 88. An inwardly directed annular boss 88 is similarly provided on the inside of `the conductor 80 for engagement with the conductor 8|. The conductor 8| is slotted, as shown at |18,l in order to permit compression; which angular movement at the Joint tends to produce, without deforming the conductor 80 or its associated parts. Preferably two or more slots such as the slot 98 are provided. The conductor 98 may also be slotted in the neighborhood of the boss 81 although this precaution is usually unnecessary because angular movement at the joint decreases the contact between the conductor 88 and the boss -81 instead of increasing it as in the case of the conductor 8| and the boss'il. It is not necessary to maintain any particular quality of contact between the boss 81 and the conductor 83. in accordance with the principles controlling the present invention, so that slottingof the conductor 83 for spring contact becomes an unnecessary measure. An annular sleeve-type member |88 corresponding in function to the cup-like member 20, 88 and 1| of Figs. 5, 6 and 7, is mounted upon the outside of the conductor 88 at the extremity of the latter. In order that the apparatus of Fig. 12 may be sumclently cornpact the sleeve member |88 is only slightly greater in its radial dimension than the conductor 88, so that the annular space lill between the back part of the sleeve member |88 and the conductor 88, which corresponds to the branch channel 1 of Fig. 1, is quite narrow. Because of the extreme narrowness oi this space, and the increased end effect resulting at the cavity mouth, the depth of such space necessary to produce resonance at the desired frequency (i. e. an electrical quarter-wave length) is considerably shorter than one-quarter of the Wave length of the corresponding electromagnetic waves in air. Thus for an apparatus of the configuration of Fig. 8 for operation in the range between 5 and centimeters (i. e. for operation in the neighborhood of some particular frequency at that range) a depth of approximately 0.15 times the wave length in air is suitable. The electrical quarter-wave length at the same frequency in the annular channel |02 between the sleeve member |08 and the conductor 88 is somewhat longer, being approximately 0.22 of the wave length in air. The sleeve member |08 consequently has an ample surface of contact with the outer surface of the conductor 88 for the establishment of a good mechanical and electrical Joint.

' IIn a similar manner. an annular sleeve member |08 is mounted near the extremity of the conductor on the inner side of the latter conductor facing the conductor 8|. 'I'he sleeve member |08 is so shaped as to provide an annular space or cavity |08 having essentially the same properties as the cavity |0| and to establish an annular channel |01 between the conductor 8i and the sleeve member |08. In accordance with the previously explained principles of the present invention, the sleeve structure |00 cooperates with the neighboring walls of the conductors 88 and 88 to create an apparent radio frequency short circuit at the annular mouth |'8 of the channel |82 while the sleeve member |08 cooperates with the neighboring walls of the-conductors 80vand 8| to establish an apparent radio frequency short circuit across the annular mouth |I'| of the channel |81.

I'hus at the frequency of operation of the apparatus the conductor 18 is brought into energytransferring relation ,with the conductor 8| through the conductor 80, and the conductor 18 is brought into energy transferring relation with the conductor 82 through the conductors 88, 88,

, 98 and 82.

In order that the `ioint shown in Fig. .l2 may be employed for connecting transmission lines in a system in which the air pressure inside the transmission lines is maintained above the pressure of the atmosphere outside them, a Sylphon bellows ||2 is provided around the joint. One end of the Sylphon bellows ||2 is soldered onto the annular'structure 81 while the other end is soldered onto the annular structure 88.

Fig. 13 shows an arrangement for establishing an apparent radio frequency short circuit in accordance with the principles of the present invention for the purpose of filtering the radio frequency current from the intermediate frequency output of a heterodyne mixer or first detector apparatus. The heterodyne mixer apparatus shown in Fig. 13 comprises a coaxial type resonator having an outer housing H5 and an inner cylindrical column |18 and comprises also a rectifier element ||1 which may be and preferably is a cartridge containing a silicon crystal and associated "cats Whisker" wire. Such crystal and wire when adjusted are held in place by wax and are enclosed in a cartridge having suitable electrical contact surfaces at the end and an outer body portion composed of insulation as shown generally at ||1. The rectifier element ||1 is mounted between a suitable recess H8 in the outer housing I I8 and a clip H8 electrically connected to an inner conducting structure |20, |2I, |22 which is located inside of and insulated from the cylindrical structure H8. The housing ||5 constitutes a resonator and is provided with an adjustable plug |28 for purposes of tuning and is adapted to be excited by signal voltage and local oscillator voltage through suitable coupling arrangements not shown in Fig. 13. It is Vdesired that the voltage appearing across the crystal may be impressed upon an intermediate frequency amplifier which may be connected to the wire 17 |22, but it is also desired that the voltage of signal and local oscillator frequencies appearing across the crystal shall notvappear across the intermediate frequency amplifier ybut that the radio and local oscillator frequency currents may complete their circuit in the resonator"||5, H5. For this reason it is desirableto establish an apparent radio short circuit between the upper part of the conducting element |2| and the cylindrical structure IIB. For this purpose thev lower part of-the conducting structure |2| is provided with a cavity surrounding the wire |22, which cavity is preferably illled with a mass |23 of solid dielectric, such as polystyrene. 'I'he axial dimensions of the mass of dielectric |23 and of the cavity whlch it lls issubstantially an electrical quarter-wave length. Thus at a distance oi an electrical quarter-wave length up from the bottom of the metallic structure |2| an apparent radio frequency short circuit will appear between the structure |2| and the structures H0. This apparent short circuit is preferably made to occur in the neighborhood of the clip H9. A| which is carried in a hole drilled in the structure |2|. At the intermediate frequency produced by the interaction of the signal and local oscillator frequencies there is of course no such apparent short circuit so that the intermediate frequency voltage can be utilized to excite an intermediate frequency ampliiier. The apparent `radio frequency short circuit is of great importance for the successful operation of the device, for the local oscillator would otherwise pass 'radio frequency oscillations to the intermediate `frequency amplifier which would result in considerably increased noise in the amplifier.

In order to provide the desired insulation between the structure I 2| and the structure IIB, insulation is provided as shown at |25, and |21. A metal `cap 4|28 threadedonto the lower part of the structure I| 8 cooperates with the insulating washers |26 and |21 and with a ridge |29 suitably located on the outside of the structure |2| in order to maintain the parts in the desired alignment and position. 1 Fig. 14 illustrates the application of the principles of the present invention for the formation of a joint between two sections of wave guide pipe. The 'ends of two sections of cylindrical wave guide .pipe having metal walls are shown in axial cross section at |30 and |3|. The pipe- |30 is provided with a terminal ilange structure |32 and the pipe |3| is provided with a simple perpendicular terminal flange |33. When the flange structure |32 and the flange |33 are fastened together. as by clamping arrangement not shown in the figure, in such a manner as to bring the guide pipe ,|30 and |3| into axial alignment, an annular gap 4|35 is left between the` extremities of the pipes |30 and |3|. The ilange structure |32 is so built that the gap |35 is extended into an annular recess |35 which at a distance oi an electrical quarter-wave length from the mouth of the gap |35 leads into an annular groove |31 having a depth of an electrical quarterwave length. Except for the development in annular shape, the structure of Fig. 14 is exactly analagous to that shown lin Fig. 3. The groove |31, for instance, corresponds to the branch channel 1 of Fig. 3. Instead of the definite gap shown in Fig. 3 at 6b there is in the arrangement of Fig. 14 only the contact boundary between the ilange structure |32 and the ange |33, but since the existence of electrical contact at this location is essentially immaterial, this difference is not of great importance. If desired, a thin layer of inthe fball bearings mounted in the races |411' and |42, the structure shown in Fig. 15 is analogous to that in Fig. 14. The wave guide pipes between -which the rotating Joint 'is provided are shown at and |46 and a small gap between them appears at |41 which extends into the radial channel |43, which Y corresponds to the. channel |36 of Fig. 14. Instead of being directly closed oi as in Fig. 14, the channel |48 continues beyond the branch channel |49, which corresponds to the groove |31, in order that the only contact between the relatively rotating structure may be at the ball bearings, thus reducing friction. In accordance with the principles of the present invention, the branch channel or groove |49 has a depth equal to an electrical quarterwave length and the distance -from the intersection of the branch channel |43 with the radial channel |40 to the mouth |41 of the radial channel |48 where it opens into the cylindrical wave guide system is also an electrical quarter-wave length. Although in Figs. 14 and 15 the wave length of the oscillations in the cylindrical waveV guide system may be considerably longer than the wave length of oscillations of the same frequency in unconilned air on account of the difference in the form of the wave, the electrical quarter-wave lengths in the structure |36, |31 and the structures |48, |49 closely approximate one-quarter of the wave length of oscillations of the said frequency in open air, which may be lexplained iby the fact that in these annular struc' tures the waves are oi the transverse electro. magnetic variety. y

' Grooved ange structures such as those shown in Figs. 14 and 15 might also be used in cooperation with a movable metallic closure, such as a disk rotated on an axis outside the wave guide and having perforations adapted to open the wave guide when they are in registry with the wave guide cross section, thereby/constituting a switch or wave guide valve. A single rotating disk mayv be arranged to switch several wave guides alternately.

Fig. 16 shows the application of the present invention for the construction of an improved form of terminating closure for a rectangular wave guide pipe. The rectangular wave guide |50 is shown in longitudinal cross section. The plane of the view is perpendicular to the broader side of the wave guide pipe. The wave guide pipe |50 is designed to transmit electromagnetic f waves in its interior which are of the 110,1 mode,

known 'also as the TEo,1 mode, so that the electric vector of such oscillations in the pipe will be directed perpendicularly to the broader sides of the pipe which appear in Fig. 16 at the top and bottom. The electric vector will consequently lie in the plane of the ligure. oriented in a vertical direction. The provision of an adjustable conducting closure in a wave guide pipe such as the pipe |50 has heretofore presented a considerable problem because extremely'good electrical contact was necessary to prevent excessive losses at the contact zone'and extremely good electrical .contact was diillcult to obtain in an adjustable i9 device. In the arrangement shown in Fig. l the necessity of extremely good electrical contact between the terminating closure and the walls of the wave guide pipe is avoided. y The terminating closure shown in Fig. 16 includes a sliding guide portion which may conveniently be a block of metal, and a suitably shaped plunger or piston |52 mounted on.' the block |5i in such a manner as to clear the upper and lowerA surfaces of the wave guide pipe |50 without electrical contact therewith and having a flat front surface |53 which acts as a conducting terminating surface closing ofi' the pipe wave guide 55d. A threaded handle |5i is fastened on the back of the block |5| and is adapted to be operated by a suitable threaded adjusting mechanism for adjusting the location of the closure apparatus and particularly of the terminating surface |53.

Because the electric vector is vertically oriented in the plane of the paper with respect to Fig. 16, there is n-o problem of contact losses at the lateral edges, not shown, of the terminating surface Q55 and these may thus rest in contact with the narrow walls of the wave guide EEES (the vertical walls with respect to Fig. 1G). itt the top and bottom edges of the surface |52, however, the appli-cation of the present invention is desirable in order to provide the desired radio -frequency conducting relation between the surface |53 and the upper and lower walls of the wave guide tt. The piston 552 is accordingly provided with two cavities ist and i5@ which communicate at their rear ends with the clearance spaces le? and itt respectively through slots |59 and itt. The slots |59 and it@ open respectively into the clearance spaces itt and itt at a distance of an electrical quarter-wave length Ifrom the front surface itt of the piston 52. Likewise the electrical length of the cavities ite and |55, including the contribution of slots |59 and itil respectively, is also a quarter-wave length. The desired radio-frequency short circuit is therefore established in accordance with the principles already outlined of the present invention, the clearance spaces iet and itt corresponding to the gap t oi Fig. i and the cavities |55 and |55 corresponding with the bran-ch channel i of Fig. 1.

The electrical quarter-wave lengths here in question differ in their relation. to the correspending wave length in air from the example heretofore given, on account of the different configuration of the resonators which in this case are rectangular in shape instead of annular, so lthat the waves in the cavities are probably of the longer-wave-length Hna mode instead of transverse electromagnetic." For rectangular wave guides for operation at frequencies for which the wave length in the guide is about one and onehalf times the wave length in free space, a terminating closure such as that shown in Fig. 16 is preferably provided with a plunger so shaped that the channels |57 and |58 have a length from the surface |53 to the nearer edge of the slots |59 'and |80 of approximately one-third the wave length in air previously defined. The longitudinal dimension of the cavities |55 and |55 from their forward end to the nearer edge of the slots |59 and |6|l is preferably approximately 0.28 times the said wave length in air. As previously explained, both these dimensions are electrical quarter-wave lengths, it being understood that the electrical quarter-wave length relating to the cavities |55 and |56 is so defined as to include the contribution of the slots |59 or |60 respectively.

Vin a wave guide pipe.

In the apparatus of Fig. 16 it'is undesirable to leave the lateral terminations of the cavities |55 andA |56 closed olf merely by the vertical walls of the wave guide |50. Since some of the circulating current of the resonant cavities might in such case be allowed to iiow across the zone of doubtful contact between the plunger |52 and the lateral wall of the wave guide |59, the cavities |55 and |56 are instead closed off by a structure electrically integral with the plunger |52. This may be provided by soldering two lateral sheet metal walls (the edges of one of which appear in Fig. 16 at iti and |62 respectively) on the lateral faces of the plunger or piston |52. These sheet metal side pieces of the piston itt may slide in flush contact with the vertical walls of the wave guide |50, or may be slightly spacedv therefrom. These sheet metal side pieces are indicated in Fig. 16A Iby numerals |53 and itt.

Figs. 1'7 and 18 show the application of the .present invention in the `construction of devices for applying an adjustable loading capacitance Wave guide pipes are shown at |65 in Fig. 17 and it@ in 18. These wave guide pipes are of the rectangular type (but round Ipipe could, of course, also be used) and are shown in a longitudinal cross section corresponding to that of the wave guide pipe itt shown in Fig. 16, Iso that the electric vector of the oscillations intended to be transmitted by the pipes i655 and itt lies in the plane of the figure in a vertical orientation. In many wave guide pipe systems it is desirable to introduce an adiustably projecting metallic meinber which projects through either the upper or lower wall of the wave guide and thus acts as a loading capacitance. In order to reduce undesired losses arising from the charging current of the loading capacitance it is advantageous to apply the principles of the instant invention for establishing an apparent radiofrequency short circuit where the loading capacitance element passes through the plane of the inner conducting surface of the wave guide wall. In Fig. 17 the capacitance loading ele-ment is a rod itt" which is adapted to be advanced or retracted with respect to the wave guide wail by manipulation of a knurled knob i638 cooperating with screw threads M59. The element it? is mounted in the supporting structure Htl which is itself mounted on the wall of the wave guide ite. A set screw ill is provided for maintaining an' adjustment of the apparatus which it is desired to fix. .A cylindrical cavity H2 is provided in the lower end of the housing ill) surrounding the rod element iti. At the mouth of this cavity is 4mounted. (preferably by soldering) a sleeve mem ber |13 which extends upwards into the cylindrical lcavity |12 dividing it into two 'annular spaces which are respectively the annular channel llt, between the rod element itl and the sleeve member |13, and the annular chamber |15 which is closed at the bottom, as at |16, by the part of the sleeve member |73 which is fastened to the housing |10 near where the latter is mounted upon the wave guide wall. The annular spaces lit and |15 communicate at their upper extremities over the upper edge of the sleeve member |13 which does not extend so far upward as to come in contact with the top of the cavity |72. In accordance with the principles of this invention the electrical length of the annular gap llt is made substantially equal to an electrical quarter-wave length and the electrical length of the annular cavity |15, including that part of the 21 cavity I 12 which connects the cavity |15 with the annular gap |14, is also made substantially equal to an electrical quarter-wave length.v In apparatus of the configuration of Figs. 17 and 18 such electrical quarter-wave lengths closely approximates one-quarter of the wave length in air." On account of the configuration of the structures |13, |14, |15 and its associated element, therefore, an apparent short circuit appears at the desired radio frequency between" the rod element |81 and the bottom surface of the sleeve element |13 which is electrically integral with the upper wall of the wave guide |65. Thus a good radiol frequency connection is established between the part of the rod |61 projecting into the wave guide and the wave guide wall irrespective of the nature of the electrical contact that may exist at the screw threads |69.

Fig. 18 shows a structure similar in principle to that shown in Fig. 17. The rod |18 provides an adjustable loading capacitance in the same manner as does the rod |61 of Fig-17. 'I'he housing |18 is essentially similar to the housing |18 and the sleeve structure |80 corresponds to the sleeve |13. The cavities and clearance surrounding the sleeve member |80 are organized in the same manner as the corresponding cavities and clearances shown in Fig. 17 around the sleeve member |13 with the -result'that at the desired frequency of operation an apparent -short circuit appears between the rod member |18'and the bottom surface of the sleeve member |80 which is electrically integral with the upper wall oi' the wave guide |66. Instead of the knurled knob |88 and the set screw |1| of Fig. 17 diiferent means are provided in Fig. 1,8 for making the adjustment of the loading capacitance. The upper part ofthe rod |18 does not extend above the screw-threaded portion of the housing |18 but is provided with a slotted upper surface for engagement with a screw driver. the slot being shown at |8|. The upper part of the rod |18 is crystal cartridge |81 and the nearby portions of the upper wall of the wave guide |85. On the other hand lt is desired that the clipl |81 should be isolated from the wave guide |85 and its associated structure for all frequencies inthe range of the intermediate frequency which the crystal rectifier element |91is adapted to generate when oscillations of signal and local oscillator frequency are introduced into the wave guide |85.

The clip |88 is insulated from the wave guide |85 and its associated structure by a washer |89 and a plug |80 and is mounted and supported on a metallic housing structure |9| which is preferably soldered onto tle wave guide |85 as 4shown in-Fig. 19. The lower part of the housing |9| is provided with a cylindrical cavity |92 in which is extremity of the annular threaded into the housing |19 in the same manner as the rod |61 is threaded into the housing |10. A threaded plug |82 is provided which may be screwed down on top of the rod member |18 for fixing and sealing the adjustment of the latter.

A variable inductance may be providedv in a similar fashion by orienting the rods |61 or |18 perpendicularly to the electric vector. The rod would then, in the case of rectangular wave guides,` usually be introduced through one of the narrower walls.

. Fig. 19 illustrates the application of the invention to apparatus for employing a crystal rectifier in a heterodyne mixer circuit in conjunction with a wave guide pipe system. A rectangular pipe wave guide similar to the wave guide of Fig. 16 and the wave guides |85 and |86 of Figs. 17

yand 18 isshown at |85, again in a longitudinal cross section parallel to the direction of the electric vector. A recess |86 is provided in the lower wave guide wall .for mounting a crystal rectifier cartridge |91 similar to the rectier element ||1 of Fig. 13 across the wave guide |85. The recess |86 is thus similar to the crystal mounting recess ||8 of Fig. 13. The upper end of the crystal rectier cartridge is inserted in the clip |81. As in the case of the clip ||9 of Fig. 13, the clip |81 is slotted as shown at |88 in order to provide a spring grip. In order that the radio frequency circuit may properly be completed it is desired to establish a radio frequency short circuit or lthe equivalent thereof between the upper end of the located a sleeve member |93 arranged in the samel manner as the sleeve member |18 of Fig. 17 and the sleeve member 88 of Fig. 18. Thus an annular clearance space |94 is provided around the clip |81 into which. at a 7dista-nce of an electrical quarter-wave length from the inner surface of the wave guide wall |85 is connected a branch cavity |85 having a total length of'another electrical quarter-wave length. This structure as previously explained causes an apparent radiofrequency short circuit to appear at the lower clearance space |94 for the desired frequency of operation.

In order that the apparatus of Fig. 19 may best function as a heterodyne mixer, it ls desirable to `associate tuning structures with the wave guide |85 in the neighborhood of the crystal position in order to provide conditions for maximum energy transfer between the oscillations in the wave guide |85 and the crystal circuit. For this purpose it is desirable to terminate the wave guide |85 at side of the crystal position, which may be to the right in Fig. 19 by an adjustable closure such as that shown in Fig. 16 and further to provide loading capacitances by means of arrangements such as that shown in Fig. 17, mounted on the wave guide |85 on the other side of the crystal position from the terminating closure. Holes |95 and |98 are shown in Fig. 19 in the lower wall of the wave guide |85 for mounting adjustable loading capacitance structures such as that shown in Fig. 17, it being understood that the respective housings of such structures should preferably be soldered to the Wave guide |85 in order to provide good electrical contact. Thus it may be seen that in a complete heterodyne mixer operating uith a rectangular wave guide input, this present invention may advantageously be used in four different parts ofa single mixer apparatus.

The foregoing examples of the application of Y one branch channel 1 may be provided opening into the gap 6, each of said branch channels connecting with the gap 6 at a distance of an electrical quarter-wave length from the gap 8 which communicates with the surfaces 2 and 8. Such an arrangement wouldordinarily have no special advantage since the single branch channel 1 shown in Fig. 1 and Fig. 3 is usually sufficient to produce the desired result. In one form, shown diagrammati'caily in Fig. 20, the double branch arrangement may have some advantages. In Fig.

` 20 the surfaces 2 and 3 are again'shown between which it is desired to establish a radio-frequency conducting relation. The surfaces 2 and 3 are, as in Figs. 1-4, separated by a gap t. Two branch channels l and 'la open into the gap 6. In this case the location and depth of the branch channel l is calculated to provide an apparent radiofrequency short circuit across the mouth of the gap t between the surfaces 2 and at a certain radio frequency and the location and depth of the branch channel 'la are calculated to provide such an apparent radio-frequency short circuit at a frequency slightly different from the rst-mentioned frequency. The frequencies for which the branch channels 'i and la are respectively designed are sufficiently 'close together (i. e. com mensurate in magnitude) so that for frequencies between these two frequencies only a small impedance is presented at the mouth of the gap 6. In this manner a relatively good radio-frequency conducting condition is established between the surfaces 2 and t for a range of frequencies, thus making the structure somewhat better adapted to broadband" operation than the corresponding structure of Fig. 3.

What I desire to Patent is:

l.. A `ioint providing for transfer of radio-frequency energy between two electrically conducting surfaces which includes an electrical resonator one electrical dimension of which is substantially a half-wave length for said radio-frequency, said resonator having a mouth constituted by a gap between said surfaces and located at one end of said half-wave length dimension. said resonator having also a terminating conducting wall at the other end of said dimension and being so constructed that an interruption is present in the wall of said resonator, other than said mouth, as a result of the assembly of said Joint, ocated at a place approximately an electrical quarterwave length from said terminating wall.

2. Means for establishing low impedance radiofrequency connection between two conducting surfaces, said means comprising an electrical resonator having a cavity, the walls of the cavity of said resonator being defined by conducting surfaces integral with the aforesaid conducting surfaces between which connection is desired, said cavity having an end wall locatedl at approximately an electrical half-wave length in said cavity from the location at which it is desired to cstablish the aforesaid connection. said resonator being constituted so that said first-named surfaces are in close proximity but not in contact at said last-mentioned location, and being further constituted with an interruption in the walls of said cavity between the cavity walls integral with one of said surfaces and the cavity walls integral with the other of said surfaces. which interruption is located approximately midway in said cayity4 between said end wall and the location at claim and obtain by Letters which it is desired to establish the aforesaid connection.

3. Means for establishing low impedance radiofrequency connection between two conducting surfaces, said means comprising a conducting structure defining a cavity adapted to resonate at a frequency at which such low impedance connection is desired, the walls of said cavity being defined by conducting surfaces electrically integral with the aforesaid conducting surfaces between which connection is desired, said cavity having an end wall located at approximately an integral number of electrical half-wave lengths from the location at which it is desired to establish the aforesaid connection and having a narrow mouth at said location separating said first-named two surfaces, said cavity being further provided with at least one discontinuity between the cavity wall integral with one of said surfaces and the cavity wall integral with the otheiof said surfaces, located at a distance in said cavity from said end wall of approximately an odd number of electrical quarter-wave lengths.

4. Means for establishing low impedance radiofrequency connection across a gap between two conducting surfaces. said means comprising an electrical resonator having conducting surfaces integral with the said rst mentioned conducting surfaces and defining a cavity having a mouth at said gap and having an end wall located approximately at an electrical half-wave length in said cavity from said gap, said resonator being further provided with a discontinuity between the cavity walls integral with one of said surfaces and the cavity walls integral with the other of said surfaces, situated substantially entirely at locations approximately an electrical quarter-wave length from said end wall..

5. in' apparatus for operation at radio frequency, a joint between two relatively movable conducting surfaces separated by a narrow gap, comprising relatively movable conducting structures associated with said surfaces extending said gap for a distance of at least an electrical quarterwave length from said surfaces, at least one of said structures providing a branch channel disposed perpendicularly to and communicating with said gap at a location substantially an electrical quarter-wave length distant from said surfaces, said branch channei having a length of substantially an electrical quarter-wave length and having at its extremity a conducting terminating closure.

6. In an apparatus foroperation at radio freouency, a joint between relatively movable conducting surfaces including means for maintaining a gap between saidA surfaces, relatively movable structures associated with said surfaces extending said gap uniformly for a distance of at least an electrical quarter-wave length from said surfaces, at least one of said structures providing a branch channel disposed perpendicularly to and communicating with said gap at a location substantially an electrical quarter-wave length distant from said surfaces, said branch channel having a length of substantially an electrical quarter-wave length and having at its extremity a conducting terminating closure.

7. In an apparatus for operation at radi-o lfrequency, a joint between two relatively movable conducting surfaces including means for maintaining a gap between said surfaces, relatively movable structures associated with said surfaces extending said gap for a distance of at least 2%00 of the wave length in open air corresponding to a desired frequency of operation. at least one of said structures providing la branch channel disposed at an angle to and communicating with said gap at a location distant from said surfaces by about one-quarter of said wave length, said branch channel having a length of about onequarter of said wave length and having at its extremity a conducting terminating closure.

8. A resonator for establishing a readily demountable low impedance radio-frequency connection between two conducting elements com- 25 prising a cavity resonator the walls of which are defined lby structures fixed on said conducting elements, said cavity resonator having a conduct. ing end wall substantially without loss-producing discontinuities located approximately at an electrical half-wage length inv said resonator from the location at which it is desired to establish the aforesaid connection having also a mouth at said location separating said conducting elements. and having discontinuity between that part of the walls of said cavity resonator defined by one of said conducting elements and that part of the walls of' said cavity resonator defined by the other of said conducting elements located approximately an electrical quarter-wave length in said resonator from said end wall.

9. A Jointfor'relatively rotatable coaxially adjacent wave guide conductors for facilitating transfer of radio-frequency energy across said joint, including means for maintaining a gap' between the said conductors at said Joint, relatively rotatable structures on the extremities of said conductors in the neighborhood of said gap substantially integral electrically withsaid conductors and. so shaped as to extend said gap for a distance of at least an electrical quarter-wave length from the mouth of said gap, said mouth ,animo Y transmission line, said outer conductor ioint in-- cluding a sleeve located outwardly of one of said outer conductors and spacedfrom said conductor except at and near the extremity of the latter where it is joined thereto by a conducting structure. said sleeve being of such dimensions as to enclose between itself and said conductor a cavity having an axial dimension of an electrical quarter-wave length with respect yto a desired radio frequency of operation, and a conducting surface associated with the other of said outer conductors disposed so as to define between itself and said sleeve an annular clearance space having la length of at 'least an electrical quarter-wave length and communicating with said cavity at a distance of substantially an electrical quarterwave length from the extremity of said clearance space nearest the eii'ectlve location of said outer conductor joint; said inner conductor joint comprising a central recess in one of said inner conductors and a projection of the other of said inner conductors extending within said recess to such a distance that the annular clearance space between said inner conductor has a length offsubbeing defined as the opening of said gap at the current-carrying surfaces of said conductors. said conductors having a configuration providing also for a branch channel having a depth of substantially an electrical quarter-wave length disposed 'perpendicularly to and communicating with said gap at a distance from said mouth of substantially an electrical quarter-wave length.y

10. A- Joint for tubular conductors for facilitating transfer of radio-frequency energy across said joint, including means for maintaining a gap between the said conductors at said joint, a cy-v lindrical sleeve' mounted on one of said conductors and spaced from said conductor except near the extremity of the latter where it is joined thereto by a conducting structure. said sleeve enclosing between itself and said conductor a mass of solid dielectric and thereby defining an electrical resonator having an axial dimension oi' an electrical quarter-wave length with respect to -a desired radio frequency of operation, and a conducting surface associated with the other of said conductors adapted to extend the said gap between said conductors at said joint withoutA substantial changes in clearance for a distance of at least an electrical .quarter-wave length to form an annular clearance space between said surface and said sleeve, said sleeve andsaid conducting surface bein-g so dlmensioned that said resonator communicates with said annular clearance space at a distance from said gap at said joint of substantially an electrical quarter-wave length.

11. A joint for cylindrical conductors in accordance with claim 9 which includes means providing rotation of at least one of said conductors about the axis thereof.

12. A .ioint'for tubular conductors in accordance with claim l0 which includes means providing for relative axial rotation of the members of said joint.

13. A joint for coaxial conductor transmission lines for operation at radio frequency including projection extending therein.

stantially an electrical quarter-wave length with respect'to said frequency. said recess being deeper by a substantial amount than the length of said 14. A joint for coaxial conductor transmission lines in accordance with claim 13 which includes means providing for relative axial rotation of the respective coaxial conductor transmission lines constituting the elements of said joint.

15. Means for promoting transfer of radiofrequency energy between two electrically conducting surfaces for a range of radio frequencies, said means including structures associated with said surfaces, maintaining a narrow gap between said surfaces, defining an electrical wave guide of relatively low characteristic impedance communicating with said gap and defining also a branch wave guide of relatively high characteristic impedance, with a short-circuit termination and of a depth of an odd number of electrical quarter-wave lengths, said branch wave guide communicating with said first-mentioned wave an outer conductor joint and an inner conductor Joint, and including means for maintaining a gap between the respective outer conductors of the said transmission line and forvmaintaining a gap between the respective inner conductors of said guide at a location an odd number of electrical quarter-wave lengths from said gap.

16. Means for promoting transfer of radiofrequency energy between two electrically conducting surfaces for a range of radio frequencies,

said means including structures associated with said surfaces, maintaining a narrow gap between said surfaces, defining an electrical wave guide of relatively low characteristic impedance com municating with said gap and defining also an additional waveguide of relatively high characteristic impedance, with a short-circuit termina- -tion and of a depth of an electrical quarter-wave length, said additional wave guide communicating with said first-mentioned wave guide at a location an electrical quarter-wave length from said gap, said first-mentioned wave guide having no substantial interruptions in its walls between said gap and said additional wave guide.

17. Means for promoting transfer of radiofrequency energy between two electrically con.

of ai characteristic impedance substantially higher than that of said first-mentioned wave guide and likewise adapted to entertain transverse electromagnetic waves, said additional wave guide having a short-circuit termination, having a length of an electrical quarter-wave length and communicating with said first-mentioned wave guide at a location an electrical quarter-wave length from said gap.

18. A joint according to claim 6 in which the branch channel is 'such as to exhibit a characteristic impedance to the propagation of oscillations therein substantially higher than the corresponding characteristic impedance of said gap.

19. A joint according to claim 7 in which the branch channel is substantially wider than the gap with which it communicates and is thereby adapted to provide a discontinuity in one wall of the gap which is substantially of the open-circuit type fora relatively wide range of frequencies.

20. A rotating joint for tubular conductors for facilitating transfer of radio-frequency energy across said joint, including means for maintaining a gap between the said conductors at said joint, structures on the extremities of said conductors in the neighborhood of said gap substantially integral electrically with said conductors and so shaped as to extend said gap for a distance effectively of an electrical quarter-wave length from the mouth of said gap, said mouth being defined as the opening of said gap at the current-carrying surfaces of said conductors, said conductors having a configuration providing alsol for a branch channel having a depth of substantially an electrical quarter-wave length and communicating with said gap at a distance from said resonator; said inner conductor joint comprising a central opening in one of said inner conductors and a projection of the other of said inner conductors extending in spaced non-contacting relationship within said opening.

23. A rotating electrical joint for coaxial transmission lines including an outer conductor joint an an inner conductor joint, means for maintaining an axial gap between the outer conductors of said lines at said joint, said outer conductor joint including a cylindrical sleeve secured to the outer surface of one of said outer conductors and defining an annular cavity between itself and the outer surface `of said one conductor. said cavity being closed at the end adjacent said gap and extending axially therefrom a distance of approximately a quarter wave length oi the desired frequency of operation, and a conducting surface associated with the other outer conductor disposed so as to dene between itself and said sleeve an annular clearance space of at least an electrical quarter-wave length, said clearance space communicating with said cavity and said gap; said` inner conductor joint comprising a cenmouth effectively of an electrical quarter-wave length.

21. A rotating joint for tubular conductors for facilitating transfer of radio-frequency energy across said joint, including means defining a gap between the said conductors at said joint, structures on the extremities of said conductors in the neighborhood of said gap substantially integral electrically with said conductors and so shaped as to extend said gap for a distance effectively of an electrical quarter-wave length from the mouth of said gap, said mouth being defined as the opening of said gap at the current-carrying surfaces of said conductors, said conductors hav ing a configuration providing also for a branch in one of said structures, said branch having a depth of substantially an electrical quarter-wave length and communicating with said gap at a distance from saidlmouth effectively of an electrical quarter-wave length. I

22. A rotating electrical joint for coaxial transmission lines including an outer conductor joint and an inner conductor joint, means for maintaining an axial gap between the outer conductors of said lines at said joint, said outer conductor joint including a cylindrical sleeve secured to the outer surface of one of said outer conductors and enclosing between itself and said one conductor a mass of solid dielectric, said sleeve and said mass of dielectric being of a dimension less than a, quarter-wave length of the desired frequency of operation but defining a resonator having an axial length of an electrical quarterwave length of said frequency, and a conducting surface associated with the other outer conductor disposed so as to define between itself and said sleeve an annular clearance spacel of at least an electrical quarter wave length, said clearance space communicating between said gap and said trai opening in one of said inner conductors and a projection of the other of said inner conductors extending in spaced, non-contacting relationship within said opening.

24. A rotating electrical joint for coaxial transmission lines including an outer conductor joint and an inner conductor joint, means for maintaining an axial gap between the outer conductors of said lines at said joint, said outer conductor joint comprising, a first cylindrical sleeve secured to the outer surface of one of said outer conductors extending across said gap and enclosing an annular clearance space between itself and the outer surface of the other of said outer conductors, a second cylindrical sleeve secured to the outer/ surface of said one conductor and enr closing an annular cavity between itself and the outer surface of said iirst sleeve, said cavity being closed at the end adjacent said gap, said cavity and said annular clearance each being of approximately an electrical quarterwave length; said inner conductor joint comprising a central opening in one of said inner conductors and a projection of the other of said inner conductors extending in spaced, non-contacting relationship within said opening.

25. A rotating joint for tubular conductors for facilitating transfer of radio frequency energy across said joint, including means for maintaining a gap between said conductors at said joint, structures secured to the extremities of said conductors adjacent said gap substantially integral electrically with said conductors and so shaped as to extend said gap for a distance effectively an electrical quarter-wave length from the mouth of said gap, said mouth being defined as the opening of said gap at the current carrying surface of said conductors, one of said structures having a groove cut therein providing a branch channel having a depth of substantially an electrical quarter-wave length and communicating with said gap at a distance from said mouth effectively of an electrical quarter-wave length, said structures further being in mechanical, but

poor electrical contact on a surface further re,

moved from said mouth than the location of said branch channel.

WINFIELD W. SALISBURY.

(References on following page) 29 N be um r REFERENCES CITED 2,321,521 The following references are of record in the 2,332,952 le of this patent: 2,351,895 UNITED STATES PATENTS '5 214001777 2,401,344 Number Name Date 2,404,086 2,155,508 Schelkuno Apr. 25, 1939 2,407,318 2,190,668 Llewellyn' Feb. 20, 1940 2,434,925 2,226,479

Pupp Dec. 24, 1949 h) Name l l Date Salinger June 8, 1943 Tischer et al Oct. 26, 1943 Allerding June 20, 1944 Okress May 21, 1946 Espley 1 June 4, 1946 Okress et; a1 July 16, 1946 Mieher et al Sept. 10, 1946 Haxby 1 Jan. 27, 1948 

